Electric heaters

ABSTRACT

An electric heater, particularly for use in a xerographic system, having a frame defining a rectangular opening, and a plurality of reaches of ribbon resistor spanning one pair of opposed walls defining the opening. A plurality of support members span the other pair of opposed walls. The resistor ribbon is extremely thin to generate heat quickly when an electric current is passed therethrough, and is transversely corrugated. The support members extend transversely of the ribbon reaches at places spaced longitudinally thereof and each support member comprises a pair of supports which engage opposite sides of the ribbon.

United States Patent Drugmand et al. 1 June 27, 1972 1 ELECTRIC HEATERS 3,053,962 9/1962 Cerasam et a]. ..2l9/216 72 Inventors: Lester D. Drugmand; John F. Volker, both g'ggg'jgg 5/1963 of Pittsburgh Pa 1969 Jann1ng....

3,522,415 8/1970 Eisler ..2l9/347 X [73] Assignee: Emerson Electric Co., St. Louis, Mo.

FOREIGN PATENTS OR APPLICATIONS [22] Filed: Feb. 22, 1971 153,368 1/1920 Great Britain ..219/532 [211 PP N91 117,361 557,674 8/1932 Germany ..219/5 32 521 US. Cl .219/532, 219 542, 338/280, Primary arg1iner\{ol ody y y y 33 2 7 333 291 33 /319 AttorneyM1chael W1ll1ams 51 1111. C1. .1105!) 3/06 [58] Field ofSearch ..219 532, 388, 216, 347, 542; 1 1 ABSTRACT 338/280, 283, 284, 287, 2913 33 An electric heater, particularly for use in a xerographic l J system, having a frame defining a rectangular opening, and a plurality of reaches of ribbon resistor spanning one pair of op- [56] References cued posed walls defining the opening. A plurality of support mem- UNITED STATES PATENTS bers span the other pair of opposed The resistor ribbon 1s extremely thin to generate heat quickly when an electnc 6 I Dmkey X current is therethrough and is transversely corrugated 3,136,835 6/1964 Hynes X The support members extend transversely of the ribbon 3,309,499 3/1967 can -338/319 X reaches at places spaced longitudinally thereof and each sup- 2,896,004 7/1959 Duffy et al ..13/22 port member comprises a pair f Supports i h engage 1,464,125 1/ 1922 Kiellgren ..338/383 X posite Sides fth ribbon 1,842,972 1/1932 lpsen et al. .....338/280 2,173,263 9/1939 Nier ..2 19/532 X 6 Claims, 14 Drawing Figures PATENTEDJUNZY ISYZ 3.673.387

INVENTORS LESTER D.DRUGMAND JOHN F. VOLKER A TTOAMF) PATENTEnJmm m2 SHEET 2 BF 3 m m E mw yww M R 507% m!m.

LESTER D. DRUGMAND JOHN F. VoLKER A TTOPNE 7 "IPATENTEDJUHZY m2 3.673.387

SHEET 30F 3 INVENTOR5 LESTER D. DRUGMAND JOHN F. VOLKER A T rox wa ELECTRIC HEATERS BACKGROUND AND SUMMARY Xerography has gained wide commercial success as a convenient and accurate method of copying printed matter and the like. The application of electric heat to afiix xerographic powder images to copy paper has been extensively used, but problems have been encountered in the design of suitable heaters because of the requirement that heat be produced almost instantaneously when the image is to be fused to the copy paper. The heater design requires an electric resistance of fine wire or very thin ribbon, and suitable support of such resistance has been difiicult.

By the use of a very thin ribbon resistance, and particularly a corrugated ribbon, and suitable support of such ribbon at a plurality of places spaced throughout its span, we have developed a heater that will withstand prolonged use and accordingly, the principal object of our invention is a new and improved electric heater of the character later to be described.

DESCRIPTION OF THE DRAWINGS In the drawings accompanying this description and forming a part of this specification, there is shown, for purpose of illustration, an embodiment which our invention may assume, and in these drawings:

FIG. I is a side view of our improved heater, showing it in general relation with a part of a xerographic apparatus,

FIG. 2 is a plan view corresponding to the line 2-2 of FIG. I,

FIG. 3 is an enlarged view of a side of the heater, as designated by the line 3-3 of FIG. 2,

FIG. 4 is an enlarged, sectional view corresponding to the line 4-4 ofFlG. 2,

FIG. 5 is an enlarged, fragmentary sectional view corresponding to the line 55 of FIG. 2,

FIGS. 6 and 7 are enlarged, sectional views respectively corresponding to the line 66 and 7-7 of FIG. 5, showing the warping of the resistor ribbon under certain conditions of heat, 1

FIG. 8 is an enlarged, fragmentary perspective view showing the support for the resistor ribbon,

FIG. 9 is a fragmentary, perspective view of a corrugated resistor ribbon which is particularly suited for use in our improved construction,

FIG. 10 is an enlarged sectional view showing the support of the corrugated resistor ribbon,

FIG. 11 is an enlarged sectional view of a detail, corresponding to the line 11-11 of FIG. 1,

FIG. 12 is a separated perspective view showing a single terminal assembly,

FIG. 13 is a separated perspective view showing a double terminal assembly, and

FIG. 14 is an enlarged, fragmentary sectional view which is taken along the resistor ribbon in either one of the terminal assemblies.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring particularly to FIG. 1, the improved electric heater is disposed in position to fuse a powdered image on copy paper C moving along rollers R. In the disclosed embodiment, the heater comprises a metal frame 21 providing a rectangular opening 22. The frame has a first pair of opposed legs 23--23 and a second pair of legs 24-24, and apertured tabs 25 are formed to provide means for securing the heater to a suitable support in the xerographic apparatus.

The legs 23-23 are slit at 26 so that walls 27 may be turned upwardly and at a right angle to the legs. The legs 24-24 are slit at 28 so that walls 29 may be turned upwardly and at a right angle to the legs. The walls 27 of the legs 23-23 are provided with slots 30 (see especially FIGS. 12 and I3), and ceramic blocks 3| fit in such slots. Each block is wider than a respective slot and is formed with side grooves 32 to slidably receive wall portions margining the sides of a slot, each block seating on the lower margin 33 of the slot. The slot wall portions are slit at 34 so that tabs 35 may be bent at an angle to the wall portions to lock the bushing in the slot.

Single and double terminal members 36,37, respectively, are supported by the ceramic blocks 31. In the embodiment herein disclosed, and with particular reference to FIG. 2, there are two single temtinals 36 and six double terminals 37.

A single terminal 36, as best shown in FIG. 12, comprises a head portion 38 and a tail portion 39 which is of reduced width to form a shoulder 40. The tail portion 39 extends through an opening 41 in a respective ceramic block 31 so that the shoulder 40 abuts one face of the block and a portion 42 (shown in dotted lines in FIG. I4) is struck from the tail portion and abuts the opposite side of the block to lock the two together. Side portions of the head portion 38 are displaced up and down as shown at 43, so that the shoulder abutment with the block has considerable stability. The head portion 38 is formed with a rectangular opening 44 to pass the end of a resistor ribbon 45.

In order to produce heat almost instantly when electrical energy is passed through the resistor, the latter is made extremely thin, as-for example, about 0.00l inches thick, and is about one-fourth inches wide. The fragile nature of the resistor ribbon presents problems in connecting it mechanically and electrically to the terminal. In a preferred mode of connecting the ribbon to the tenninal, the ribbon end is caused to underlie the head portion 38 (in the position of parts shown in FIGS. 2 and I2) and the end is pulled upwardly through the opening 44. A securing lug 46 is then positioned so that its base portion 47 clamps the ribbon against the undersurface of the head portion 38 and a locating tab 48 also passes through the opening 44. The base portion 47 is provided with a welding projection 49 and the assembly is made by a resistance weld. The base portion 47 therefore provides for good electrical and mechanical connection with the head portion 38, and the ribbon sandwiched therebetween. The double terminal 37 includes a head portion 50 which is of the same length as the corresponding portion of the single terminal 36, but is about twice as wide. A pair of tail portions 51 extend from the head portion 50 to provide a shoulder 52 therebetween. Each tail portion projects through an opening 41 in a respective ceramic block 31 and is locked to the block in the manner previously described. The head portion 50 has a pair of rectangular openings 53, each topass a respective resistor ribbon 54. The securing lug 55 in this case is wide enough to span the width of the head portion 50 and is provided with a pair of tabs 56which pass through the openings 53. Two welding projections 57 are provided and the assembly is made in a manner similar to that described. The securing lug in this case insures that a good electrical bridge is made between the resistors 54,54.

The resistor ribbons are arranged in a plurality of reaches across the plate opening 22 and between predetermined terminals. Referring to FIG. 2, the upper ribbon reach extends between the left hand single terminal 36 and the upper right hand double tenninal 37. Further ribbon reaches extend between double terminals 37, and the lower reach extends from the left hand double terminal 37 to the right had single terminal 36. During assembly, the various ribbons reaches are pulled with a degree of tautness, so that each reach is substantially in a straight line, as shown in full lines in FIG. 5.

A plurality of supports extend crosswise of the ribbon reaches and engage the same at places spaced longitudinally of their span. In accordance with" our invention, each support comprises a pair of steel rods 70 of small diameter (see FIGS. 4, 5, 8 and 10) in overlying relation, the rods extending from one frame wall 29 to the opposite wall (see FIG. 2). Opposite ends of the rods 70 are disposed within upper-opening slots 71 'in the frame walls 29 and extend outwardly beyond the respective walls. Cylindrical ceramic sleeves 72 are disposed on the rods and the ribbon reaches are confined between the sleeves, as best seen in FIGS. 5, 8 and 10. The ends of the lower rod 70 rest on the bottom of respective slots and the ceramic sleeve 72 on the upper rod abuts the ceramic sleeve of the lower rod, with the resistor ribbon portion sandwiched therebetween. From a manufacturing standpoint, it is preferable to form the ceramic sleeves in a plurality of short sections, as seen in FIG. 2.

To hold the rods 70 against displacement from the slots 71, an elongated angle member 73 is connected to each frame wall 29. The assembly may be effected by means of a plurality of sleeve nuts 74 (see especially FIGS. 2 and 11) which are connected to a respective wall 29 to receive machine screws 75 which pass through respective openings in the angle members 73. In this relation, a leg 76 of an angle member overlies the ends of the top steel rods 70 to block their removal from the slots 71. The screw openings in the angle members may be vertically elongated, as seen in H6. 11, to provide for vertical adjustment.

As best seen in FIG. 5, each reach of resistor ribbon is supported at positions spaced longitudinally of its length. When electric current is passed through the ribbon, it will almost instantaneously reach a red heat, and will elongate because of thermal expansion, and the spaced supports will confine the elongation therebetween, as shown in dotted lines.

In some cases where a flat resistor ribbon is used, it has been found that the ribbon cups in opposite directions at sections 6 and 7, and eventually the ribbon will fracture at a place between such sections. To prolong the life of the ribbon resistor, we have found that if the ribbon is corrugated, as shown in FIGS. 9 and 10, the corrugations will provide sufficient widthwise strength to minimize the cupping action of the ribbon. The corrugations also provide gripping surfaces, which cooperate with the small diameter ceramic sleeves 72 to further insure that ribbon elongation is confined between adjacent supports.

In order to provide varying degrees of heat generated by the ribbon reaches, a conductor lead 80 (see FIG. 2) is connected to the upper left hand single terminal 36; a conductor lead 81 is connected to the lower left hand double terminal 37; a conductor lead 82 is connected to the upper right hand double terminal 37; and a conductor lead 83 is connected to the lower right hand single lead 36.

By a suitable switching arrangement (not shown) the leads 81 and 82 may be connected to a source of electrical energy; or the leads 80 and 81 may be connected to the source; or the leads 80 and 83 may be connected to the source. When the leads 81 and 82 are connected to the source, maximum wattage is produced, and the circuit comprises lead 81, through the lower left hand double terminal 37, through ribbon reaches a, b, c, d, and e, and their terminals, through the upper right hand terminal 37 and to lead 82.

When the leads 80 and 81 are connected to the source, a lesser wattage is produced, and the circuit comprises lead 80, upper left hand single terminal 36, ribbon reaches f, e, d, c, b, and a and their terminals, and through lower left hand double terminal 37 to lead 81.

When leads 80 and 83 are connected to the source, still less wattage will be produced, and the circuit comprises lead 80, upper left hand single terminal 36, ribbon reaches f, e, d, c, b, a, and g and their terminals, and to lower right hand single terminal 36 and lead 83.

We claim:

1. A quick-response electric heater, adapted for use in a xero-graphic system, comprising:

a support frame,

electric resistance means comprising a plurality of reaches extending between terminals carried by a first pair of opposed pans of said frame, the resistance means being in the form of a bare resistance metal of small cross-sectional area and therefore fragile in nature,

and a plurality of supports extending in spaced relation between a second pair of opposed parts of said frame, and crosswise of said reaches, each support comprising a pair of superimposed insulating rods of substantially circular cross section having opposite ends connected to respective ones of said second pair of opposed parts of said frame, each pair of rods engaging opposed surfaces of said reaches at substantially the same point to sandwich the latter therebetween, thereby to support said reaches against sagging at a plurality of places spaced longitudinally thereof.

2. The construction of claim 1 wherein said resistance means is in the form of a bare metal resistor ribbon, and

wherein each pair of rods engages opposed flat surfaces of said ribbon.

3. The construction of claim 2 wherein each ribbon reach is corrugated, and

wherein each pair of rods cooperates with corrugations of said ribbons to restrict thermal expansion of the ribbon in said reaches between adjoining pair of said supports.

4. The construction of claim 1 wherein each of said insulating rods is in the form of a small diameter metal rod having its opposite ends connected to respective ones of said second pair of opposed frame parts, and ceramic tubes threaded onto said metal rods and engageable with opposed surfaces of said resistance means reaches.

5. The construction according to claim 1 wherein said frame support is formed of sheet metal and said first pair of opposed frame parts are opposed sheet metal walls, each having a plurality of slots therein, with apertured ceramic bushings seated within respectives slots,

said terminals being of good electrically conductive metal,

each having one portion extending through an apenure in a respective bushing and outwardly of the space defined by said frame for electrical power connection, each terminal having a second portion extending from a respective bushing and inwardly of the space defined by said frame support and electrically connected to the adjoining end of a reach of said resistance means.

6. An electric heater for use in a xerographic system and the like, comprising a metal frame having a rectangular opening defined by opposed pairs of frame legs, one pair of opposed frame legs having slots for receiving insulating blocks, the latter being locked in respective slots by deformation of walls margining such slots, a terminal for each block, having a tail portion extending through an opening in the block and a head portion extending into the frame opening, a plurality of reaches of metal resistance ribbon, each reach spanning the space between head portions of corresponding terminals, said ribbon being in the order of about 0.001 inch thick for rapid heating and being transversely corrugated, and a plurality of support members extending crosswise of said ribbon reaches to support the same at places spaced longitudinally of their span, each support member comprising a pair of supports, one above and the other below said ribbon reaches, and each support comprising a metal rod of small diameter having its ends connected to the other pair of opposed frame legs and ceramic bushings of small diameter on said metal rods and engageable with opposite sides of the ribbon in said reaches, said ceramic bushings interengaging with the corrugations of said ribbon reaches to restrict thermal expansion of said ribbon in said reaches between adjoining pair of said supports. 

1. A quick-response electric heater, adapted for use in a xerographic system, comprising: a support frame, electric resistance means comprising a plurality of reaches extending between terminals carried by a first pair of opposed parts of said frame, the resistance means being in the form of a bare resistance metal of small cross-sectional area and therefore fragile in nature, and a plurality of supports extending in spaced relation between a second pair of opposed parts of said frame, and crosswise of said reaches, each support comprising a pair of superimposed insulating rods of substantially circular cross section having opposite ends connected to respective ones of said second pair of opposed parts of said frame, each pair of rods engaging opposed surfaces of said reaches at substantially the same point to sandwich the latter therebetween, thereby to support said reaches against sagging at a plurality of places spaced longitudinally thereof.
 2. The construction of claim 1 wherein said resistance means is in the form of a bare metal resistor ribbon, and wherein each pair of rods engages opposed flat surfaces of said ribbon.
 3. The construction of claim 2 wherein each ribbon reach is corrugated, and wherein each pair of rods cooperates with corrugations of said ribbons to restrict thermal expansion of the ribbon in said reaches between adjoining pair of said supports.
 4. The construction of claim 1 wherein each of said insulating rods is in the form of a small diameter metal rod having its opposite ends connected to respective ones of said second pair of opposed frame parts, and ceramic tubes threaded onto said metal rods and engageable with opposed surfaces of said resistance means reaches.
 5. The construction according to claim 1 wherein said frame support is formed of sheet metal and said first pair of opposed frame parts are opposed sheet metal walls, each having a plurality of slots therein, with apertured ceramic bushings seated within respectives slots, said terminals being of good electrically conductive metal, each having one portion extending through an aperture in a respective bushing and outwardly of the space defined by said frame for electrical power connection, each terminal having a second portion extending from a respective bushing and inwardly of the space defined by said frame support and electrically connected to the adjoining end of a reach of said resistance means.
 6. An electric heater for use in a xerographic system and the like, comprising a metal frame having a rectangular opening defined by opposed pairs of frame legs, one pair of opposed frame legs having slots for receiving insulating blocks, the latter being locked in respective slots by deformation of walls margining such slots, a terminal for each block, having a tail portion extending through an opening in the block and a head portion extending into the frame opening, a plurality of reaches of metal resistance ribbon, each reach spanning the space bEtween head portions of corresponding terminals, said ribbon being in the order of about 0.001 inch thick for rapid heating and being transversely corrugated, and a plurality of support members extending crosswise of said ribbon reaches to support the same at places spaced longitudinally of their span, each support member comprising a pair of supports, one above and the other below said ribbon reaches, and each support comprising a metal rod of small diameter having its ends connected to the other pair of opposed frame legs and ceramic bushings of small diameter on said metal rods and engageable with opposite sides of the ribbon in said reaches, said ceramic bushings interengaging with the corrugations of said ribbon reaches to restrict thermal expansion of said ribbon in said reaches between adjoining pair of said supports. 